1. Field of the Invention
The present invention relates to hard disk drives. More particularly, it relates to a disk drive including an ionizing source for facilitating dissipation of a static electric charge.
2. Description of the Prior Art and Related Information
A huge market exists for mass-market host computer systems such as servers, desktop computers, and laptop computers. To be competitive in this market, a hard disk drive must be relatively inexpensive, and must accordingly embody a design that is adapted for low-cost mass production. Numerous manufacturers compete in this expansive market and collectively conduct substantial research and development, at great annual cost, to design and develop innovative hard disk drives to meet increasingly demanding customer requirements.
Each of the various contemporary mass-marketed hard disk drive models provides relatively large data storage capacity, often in excess of 1 gigabyte per drive. A related attribute is the time at which this data can be accessed ("access time"). To this end, there exists substantial competitive pressure to develop mass-market hard disk drives that have even higher capacities with consistent, if not improved, data access times. Another requirement to be competitive in this market is that the hard disk drive must conform to a selected standard exterior size and shape often referred to as a "form factor". Generally, capacity and access rate are desirably increased without increasing the form factor, or the form factor is reduced without decreasing capacity.
Satisfying these competing constraints of low-cost, small size, high capacity, and rapid access requires innovation in each of numerous components or subassemblies. Typically, the main subassemblies of a hard disk drive are a head disk assembly and a printed circuit board assembly.
The head disk assembly includes an enclosure including a base and a cover; at least one disk having at least one recording surface; a spindle motor causing each disk to rotate; and an actuator arrangement. The recording surface defines a number of circular "tracks" onto which data is recorded. The actuator arrangement includes a separate transducer for each recording surface, and is movable to position each transducer relative to the respective recording surface. The printed circuit board assembly includes circuitry for processing signals and controlling operation of the drive.
Improvements in disks have given rise to increased storage capacity of the disk drive. For example, improvements in recording surface media in conjunction with actuator and transducer enhancements have increased the amount of data that can be stored on a particular data storage "track". Further, the number of available "tracks" per unit length on a particular disk (or "track density") has also increased. Taken in combination, these factors, along with other improvements, have resulted in disk drives having dramatically larger data storage capacities.
While improvements in data storage capacity are highly beneficial, other issues may arise. Namely, the access time generally increases with increased data storage capacity and/or track density. In general terms, the access time includes the time required to seek to a given track ("seek time") and the time required to detect a target sector once the given track is reached. A related concern is rotational latency, or the measure of the average time the transducer must wait for a target sector on the recording surface to pass under the transducer once the transducer is moved to the desired target track. Rotational latency is dependent upon the rotational speed of the disk.
To overcome the potential access time issues raised by larger data storage capacity, efforts have been made to increase the rotational speed of the disk. Hard drives normally spin at one constant speed. Typical speeds range from 5400 to 7200 revolutions per minute (rpm). Notably, the slower the rpm, the higher the rotational latency. Thus, regardless of data storage capacity, an increase in a disk drive rpm enhances overall performance.
The rpm capability of a particular disk drive is determined by the spindle motor. A disk drive spindle motor typically includes a central shaft, an upper bearing, a lower bearing, a stator and a rotor (or "hub"). The hub normally forms a flange to which the disk(s) is attached. The hub itself is concentrically positioned about the shaft. To this end, the upper and lower bearings maintain the hub in this concentric position such that the hub is rotatable about the shaft. The stator includes a series of coils and is concentrically positioned about the shaft, adjacent the hub. With this general configuration, the various coils of the stator are selectively energized to form an electromagnet that pulls/pushes on a magnet otherwise associated with the hub, thereby imparting a rotational motion onto the hub. With this arrangement, rotation of the hub results in rotation of the attached disk(s).
With improvements in the materials and circuitry associated with the above-described spindle motor design, it is now possible to provide a spindle motor having a rotational speed in excess of 7200 rpm, such as 10,000 rpm. While designs of this type address the access time and rotational latency issues described above, certain other concerns may arise. More particularly, in order to achieve rotational speeds in excess of 7200 rpm such as 10,000 rpm, alternative bearing designs must be used. Typically, prior art spindle motor bearings include an inner race, an outer race and a plurality of balls. These components are normally made of metal, such as steel. Often times, to alleviate vibration caused by the steel bearings, grease or other lubrication must be used. This grease may, in fact, limit the rpm capabilities by creating a small amount of friction. Additionally, steel bearings may deteriorate at a rotational speed of 10,000 rpm. To overcome these potential limitations, spindle motors incorporating bearings made of ceramic or related materials have been envisioned.
Unfortunately, use of ceramic or similar materials for the bearings may give rise to certain other problems. For example, during rotation, static electric charge is built up on the recording surface of the disk(s). Over time, this static electric charge, unless removed, creates a high voltage potential between the transducer and the rotating disk which may cause the static electric charge to discharge to the transducer, leading to potentially catastrophic results. Normally, the steel material used for the upper and lower bearings, in conjunction with a shaft made of aluminum or steel, provides a grounding source or conductive path for dissipating the potentially damaging static charge from the recording surface. In contrast, ceramic or similar materials have a high resistivity and will not provide a grounding or conductive path. In other words, a disk drive incorporating ceramic bearings cannot dissipate static electric charge generated during disk rotation, leading to errors and/or failure.
Accordingly, substantial research and development efforts have been expended to provide an improved spindle motor design that operates at speeds in excess of 7200 rpm, yet satisfactorily dissipates built up static electric charge.